Thursday, 18 August 2011

Alstonia

Alstonia (devil tree) consists of about 40-60 species (according to different authors), native to tropical and subtropical Africa, Central America, southeast Asia, Polynesia and Australia, with most species in the Malesian region.

These trees can grow very large, such as Alstonia pneumatophora, recorded with a height of 60 m and a diameter of more than 2 m. Alstonia longifolia is the only species growing in Central America (mainly shrubs, but also trees 20 m high).

The leathery, sessile, simple leaves are elliptical, ovate, linear or lanceolate and wedge-shaped at the base. The leaf blade is dorsiventral, medium-sized to large and disposed oppositely or in a whorl and with entire margin. The leaf venation is pinnate, with numerous veins ending in a marginal vein.

Alstonia scholaris in Hyderabad, India.

The inflorescence is terminal or axillary, consisting of thyrsiform cymes or compound umbels. The small, more or less fragrant flowers are white, yellow, pink or green and funnel-shaped, growing on a pedicel and subtended by bracts. They consist of 5 petals and 5 sepals, arranged in four whorls.

The fertile flowers are hermaphrodite. The gamosepalous green sepals consist of ovate lobes, and are distributed in one whorl. The annular disk is hypogynous. The five gamesepalous petals have oblong or ovate lobes and are disposed in one whorl. The corolla lobes overlapping to the left (such as A. rostrata) or to the right (such as A. macrophylla) in the bud. The ovary has 2 separate follicles with glabrous or ciliate, oblong seeds that develop into deep blue podlike, schizocarp fruit, between 7-40 cm long. The plants contain a milky sap, rich in poisonous alkaloids. The Alstonia macrophylla is commonly known in Sri Lanka as 'Havari nuga' or the 'wig banyan' because of its distinct flower that looks like a woman's long wig.

Alstonia trees are used in traditional medicine. The bark of the Alstonia constricta and the Alstonia scholaris is a source of a remedy against malaria, toothache, rheumatism and snake bites[citation needed]. The latex is used in treating coughs, throat sores and fever.

Many Alstonia species are commercial timbers, called pule or pulai in Indonesia and Malaysia. Trees from the section Alstonia produce light timber, while those from the sections Monuraspermum and Dissuraspermum produce heavy timber.

Alstonia trees are widespread and mostly not endangered. However a few species are very rare, such as A. annamensis, A. beatricis, A. breviloba, A. stenophylla and A. guangxiensis.